Drive circuit for conducting devices

ABSTRACT

A drive circuit for effecting current flow in an inductive circuit comprising a coil the circuit including a power transistor having its emitter collector circuit connected in series with the coil, an input transistor for controlling the power transistor and a resistor for providing a signal representative of the current flowing in the coil. A feed back transistor is supplied with the signal developed across the resistor and provides feed back to the input transistor whereby the mean value of current flowing in the coil will depend upon the magnitude of the input signal applied to the input transistor.

United 1 States Patent Adey DRIVE CIRCUIT FOR CONDUCTING DEVICES AnthonyJohn Adey, Ruislip, England Assignee: C.A.V. Limited, Birmingham,

England Filed: July 12, 1972 Appl. No.: 271,199

Inventor:

Foreign Application Priority Data July I3, 1971 Great Britain....32697/71 US. Cl 307/268, 307/269, 307/270, 123/148 E, 315/209 Int. Cl.H03k 5/00 Field of Search. 307/268, 269, 270; 123/148 E; 3l5/209 TReferences Cited I UNlTED STATES PATENTS 5/1962 Rugaber et al. 307/27011/1972 Huntzinger 307/27l OTHER PUBLICATIONS IBM Technical DisclosureBulletin; Vol. 11, No. 11, April 1969; by Johnson, page 1,403.

Primary Examiner-Andrew J. James Attorney, Agent, or Firml-lolrnan &Stern [5 7 ABSTRACT A drive circuit for effecting current flow in aninductive circuit comprising a coil the. circuit including a powertransistor having its emitter collector circuit connected in series withthe coil, an input transistor for controlling the power transistor and aresistor for providing a signal representative of the current flowing inthe coil. A feed back transistor is supplied with the signal developedacross the resistor and provides feed back to the input transistorwhereby the mean value of current flowing in the coil will depend uponthe magnitude of the input signal applied to the input transistor.

9 Claims, 2 Drawing Figures Mar. 5, 1974 I DRIVE CIRCUIT FOR CONDUCTINGDEVICES This invention relates to drive circuits for effecting currentflow in an inductive circuit and more particularly to a drive circuitfor a fuel control rod actuator of a liquid fuel injection pump, theactuator including an actuator coil.

The object of the invention is to provide such a circuit in a simple andconvenient form.

A drive circuit of the kind specified comprises in combination, a powertransistor having its emitter collector circuit connected in series withthe inductive circuit, an input transistor for controlling the powertransistor, means for providing a signal representative of the currentflowing in the inductive circuit, and means controlled by said signalwhereby the mean value of current flowing in the inductive circuit willdepend upon the magnitude of an input signal applied to the inputtransistor.

One example of a drive circuit will now be described with reference tothe accompanying circuit diagram.

With reference to the diagram there are provided terminals 10, 11 forconnection to the position and negative terminals of a source of d.c.supply. In addition there is provided an input terminal 12 which isconnected to the base terminal of a p-n-p transistor T1. The emitterterminal of transistor T1 is connected to terminal 10 by way of resistorR1 and terminal 11 by way of resistor R4, resistors R1 and R4constituting a potential divider which if desired may be replaced by asource of supplying having a voltage intermediate that of terminals 10and 11. Moreover, the collector terminal of transistor T1 is connectedto terminal 11 by way of resistors R2 and R3 in series.

In addition there is provided an n-p-n transistor T2 which isinterconnected in a Darlington pair, with an n-p-n power transistor T3.The base terminal of transistor T2 is connected to a point intermediatethe resistors R2 and R3 and the collector terminals of the transistorsT2and T3 are connected to one end of the coil L of an actuator. Theother end of the coil is connected to terminal 10 by way of resistor R5.The emitter terminal of transistor T3 is connected to terminal 11.Moreover, the collector terminals of transistors T2, T3 are connected toterminal 10 by way of a resistor R6 which is connected in series with adiode D1 having its cathode connected to terminal 10.

Also provided is a feedback transistor T4 of p-n-p type the baseterminal of which is connected to a point intermediate the coil L andthe resistor R5 and the emitter terminal of which is connected toterminal by way of resistor R7. The collector terminal of transistor T4is connected to the base terminal of transistor T1 and also to thecollector terminals of transistors T2 and T3 by way of the seriescombination comprising resistor R8 and capacitor C1.

In operation an increasing negative going input signal applied toterminal 12 will cause an increase in the collector emitter current oftransistor T1 and this in turn will increase the current flowing in thecollector emitter paths of transistors T2 and T3. An increasing currentwill therefore flow in the coil L and the voltage drop across resistorR5 will increase.

As a result of the increasing voltagedrop across resistor R5 the currentflowing in the collector emitter path of transistor T4 will increase andthis increase in current will tend to turn off transistor T1. Anequilibrium condition will be established at which the current flowingin the collector emitter path of transistor T4 will approximatelybalance, the input signal, and therefore the mean value of the currentflowing in the coil L will depend upon' the magnitude of the inputsignal. As the input signal increases in magnitude so also will the meanvalue of the current flowing in the coil.

Resistor R8 and the capacitor C1 are provided so that positive feedbackis applied to transistor T1. The application of positive feedbackresults in transistors T2 and T3 operating in the switching mode therebyreducing the heat dissipation therein.

A further capacitor C2 may be connected intermediate the base andcollector terminals of transistor T1. This will have the effect ofcontrolling the rate of change of current in transistor T3 therebyreducing the interference caused to other electrical circuits.

Furthermore, a further diode D2 may be connected in series with the baseterminal of transistor T4 and the point intermediate resistor R5 and thecoil L and a further resistor R9 is connected between the base terminalof transistor T4 and terminal 11. The effect of the resistor R9 anddiode D2 is to make the relationship between the value of the inputsignal'and the current flowing in the coil more linear and also lesssensitive to temperature variations.

In FIG. 2 there is shown a diesel engine 13 upon which is mounted a fuelpump 14 for supplying fuel to the engine. The fuel quantity control rodof the pump is connected to an electromagnetic actuator 15 whichincorporates the coil L of the circuit of FIG. 1. The circuit of FIG. 1is shown as a block 16 and the input signal for the circuit is obtainedfrom a signal processing circuit 17 to which a demand signal is suppliedby means of an operator control member 18. The signal supplied to thecircuit of FIG. 1 represents an actuator force demand signal and therewill also be supplied to the processing circuit 17 signals representingthe speed of the engine and also other signals, circuit 17 processingthese signals to produce the demand signal.

These other signals will usually include a signal representing thequantity of fuel being supplied to the engine.

I claim:

1. A drive circuit for effecting current flow in-an inductive circuitand comprising in combination, a power transistor having its emittercollector circuit connected in series with the inductive circuit, aninput transistor for supplying base drive to the power transistor, aninput terminal to the drive circuit, the base of said input transistorbeing connected to said input terminal so as to receive an input signaltherefrom, a resistor connected in the'emitter collector circuit of saidpower transistor and across which is developed a signal representativeof the current flowing in the inductive circuit, and negative feedbackmeans controlled by the signal developed across said resistor foropposing change in the input signal applied to the base of the inputtransistor whereby the mean value of current flowing in the inductivecircuit will depend upon the magnitude of a signal applied to the inputterminal.

2. A drive circuit as claimed in claim 1 in which the negative feedbackmeans controlled by said signal comprises a feedback transistor arrangedto provide a current supply to the base of the input transistor whichopposes the action of the input signal.

3. A drive circuit as claimed in claim 2 in which the emitter of thefeedback transistor includes a resistor in series therewith.

4. A drive circuit as claimed in claim 3 in which a positive feedbackpath is provided between the power transistor and the input transistorwhereby the power transistor and the input transistor operate in theswitching mode.

5. A drive circuit as claimed in claim 4 in which said positive feedbackpath is connected to the base of the input transistor.

6. A drive circuit as claimed in claim 5 including means for controllingthe rate of change of current in the power transistor.

7. A drive circuit as claimed in claim 6 in which said means forcontrolling the rate of change of current comprises a capacitorconnected between the base and collector of the input transistor.

8. A drive circuit as claimed in claim 5 including a diode through whichthe base of said feedback transistor is supplied with the signalrepresenting the current flow in the actuator coil.

9. A drive circuit as claimed in claim 1 in which the inductive circuitcomprises an actuator coil which forms part of an actuator for a controlmember of an internal combustion engine, said input transistor beingsupplied with a signal indicative of the force required to be exerted onthe control member.

1. A drive circuit for effecting current flow in an inductive circuitand comprising in combination, a power transistor having its emittercollector circuit connected in series with the inductive circuit, aninput transistor for supplying base drive to the power transistor, aninput terminal to the drive circuit, the base of said input transistorbeing connected to said input terminal so as to receive an input signaltherefrom, a resistor connected in the emitter collector circuit of saidpower transistor and across which is developed a signal representativeof the current flowing in the inductive circuit, and negative feedbackmeans controlled by the signal developed across said resistor foropposing change in the input signal applied to the base of the inputtransistor whereby the mean value of current flowing in the inductivecircuit will depend upon the magnitude of a signal applied to the inputterminal.
 2. A drive circuit as claimed in claim 1 in which the negativefeedback means conTrolled by said signal comprises a feedback transistorarranged to provide a current supply to the base of the input transistorwhich opposes the action of the input signal.
 3. A drive circuit asclaimed in claim 2 in which the emitter of the feedback transistorincludes a resistor in series therewith.
 4. A drive circuit as claimedin claim 3 in which a positive feedback path is provided between thepower transistor and the input transistor whereby the power transistorand the input transistor operate in the switching mode.
 5. A drivecircuit as claimed in claim 4 in which said positive feedback path isconnected to the base of the input transistor.
 6. A drive circuit asclaimed in claim 5 including means for controlling the rate of change ofcurrent in the power transistor.
 7. A drive circuit as claimed in claim6 in which said means for controlling the rate of change of currentcomprises a capacitor connected between the base and collector of theinput transistor.
 8. A drive circuit as claimed in claim 5 including adiode through which the base of said feedback transistor is suppliedwith the signal representing the current flow in the actuator coil.
 9. Adrive circuit as claimed in claim 1 in which the inductive circuitcomprises an actuator coil which forms part of an actuator for a controlmember of an internal combustion engine, said input transistor beingsupplied with a signal indicative of the force required to be exerted onthe control member.